1. Field of the Invention
This invention relates generally to orthodontic appliances, and more particularly concerns unitary metal injection molded orthodontic brackets made of a nickel free metal alloy in order to alleviate nickel allergy reactions experienced by a small fraction of the population.
2. Description of Related Art
Orthodontic appliances, such as brackets, buccal tubes and the like, are typically applied to teeth by adhering the appliances to the surface of the teeth. Such appliances typically include archwire portions for receiving an archwire and ligature elastic bands to provide corrective forces to straighten and reposition the teeth. The orthodontic appliances include a base portion adapted to conform to the shape of the teeth to which they are applied. The orthodontic appliances are subjected to tension and other stresses that can cause weakening of the bonds of the appliances to the teeth, and distortions in the structure of the appliances. The appliances are also subjected to cleaning that can erode the adhesion between the appliances and the teeth to which they are bonded, and are further stressed by normal mastication, so that it is not uncommon for such appliances to break away from teeth after bonding.
While orthodontic brackets are frequently made of plastic, their strength can be increased by forming at least portions of them from metal. The metal portions are typically small, and can be made by metal injection molding as a unitary metal part that is bonded or welded to be integral with the bracket. Such bonding or welding is also subject to structural instability. One known orthodontic bracket that is metal injection molded to have a basic monoblock unitary construction includes a base with raised posts adapted for abutting the surface of the teeth. However, the posts are shaped into mushroom shaped buttons by cold working, which can distort the microstructure and mechanical properties of the raised posts that are involved with bonding to teeth. Cold working of such structures can also be relatively expensive and complicated. It would therefore be desirable to form a unitary orthodontic bracket by metal injection molding to provide greater definition of the complicated geometry of the bracket as well as a well-defined base pattern to provide for better adhesion to a tooth, and to make the bracket structurally more sound.
The metal alloys used for making orthodontic brackets typically include nickel, which provides the brackets with improved hardness. However, allergies to nickel are quite common, so that it would be desirable to form the bracket of an alloy composition that is formulated to qualify as nickel-free, containing less than 1% nickel, in order to alleviate allergic reactions to nickel. The present invention meets these needs.